DCOM Volume I Appendix C

From Ministry of Water DCOM Manual

Appendix C: Example: Estimating the Capacity of a Storage Tank

Estimate the minimum storage tank capacity for a solar powered system assuming 40L/Min for 6.5 hours per day, a daily water demand of 15,000L and the, morning evening peak pattern from shown on table below:

Table C.1:Common Daily Percentage Consumption Patterns

Time Period Morning /Evening Peak* Mid-day Peak* Water Mission
5.00 0% 5% 5%
6.00 15% 5% 5%
7.00 15% 10% 10%
8.00 5% 5% 10%
9.00 5% 5% 5%
10.00 5% 5% 10%
11.00 5% 20% 5%
12.00 5% 15% 5%
13.00 5% 5% 5%
14.00 5% 5% 5%
15.00 5% 5% 10%
16.00 15% 5% 10%
17.00 15% 5% 5%
18.00 0% 5% 5%

Data from A /Hand book of Gravity Flow Water systems (Jordan)

Step 1: Determine the daily water demand pattern

The first step is to determine how much water will be used at different time during the day in the specific community. This can be accomplished by observing the community water collection habits. Water Demand for each time period can be calculated based of percentages obtained in the community water collecting habits. The balance is determined by subtracting the demand from the supply and adding it to the current surplus/deficiency balance.

Table C.2: Determining Supply Deficiencies

Timeperiod Percentage of Daily Use Supply(litres) Demand(Litres) Surplus/Deficiency(Litres Balance (Litres)
5.00 0% 0 0 0 0
6.00 15% 0 2250 -2250 -2250
7.00 15% 0 2250 -2250 -4500
8.00 5% 0 750 -750 -5250
9.00 5% 600 750 -150 -5400
10.00 5% 2400 750 1650 -3750
11.00 5% 2400 750 1650 -2100
12.00 5% 2400 750 1650 -450
13.00 5% 2400 750 1650 1200
14.00 5% 2400 750 1650 2850
15.00 5% 2400 750 1650 4500
16.00 15% 600 2250 -1650 2850
17.00 15% 0 2250 -2250 600
18.00 0% 0 0 0 600

Step 2: Determine the minimum tank capacity To ensure sufficient water to community, there must enough water to last until the trough of the next day. This calculation is represented as;

Vtank = Vmax - Vmin - Vfinal Vtank = 4500L - (-5400L) -600L = 9300L

The water storage tank should be able to hold at least 9300L to suffice the need of the community. The designer should use 10,000L storage tank or use two 5000L storage tank in sizing of the Capacity of Tank.